| Molecular spectroscopic and photochemical methods are used in the study of supercritical fluid properties, especially solute-solvent clustering and solute-solute clustering. For the probing of solute-solvent clustering, experimental results obtained for a series of solvent environment-sensitive fluorescent molecular probes in supercritical fluids of different polarities are presented and discussed in terms of a generalized three-density-region solvation model. The issue of solute-solute clustering is investigated by using well-characterized bimolecular reactions as probes. The results are explained in terms of a solute-solute clustering mechanism in which enhanced bimolecular reaction efficiencies are attributed to a higher local solute concentration than the bulk. The existence and magnitude of the local concentration enhancement effects on different bimolecular reactions are discussed. In addition, the photodimerization of anthracene is used to demonstrate the effect of the low density solvent environment on the chemical reaction yield in supercritical carbon dioxide.; Similarly, molecular spectroscopic methods are used to study the photophysical properties of the newly discovered fullerene materials. The fluorescence parameters including the spectra, quantum yields, and lifetimes of (60) fullerene and (70) fullerene are determined systematically and accurately. The charge transfer processes between the fullerenes and electron donors such as N,N-diethylaniline and N,N-dimethylaniline are investigated quantitatively by fluorescence spectroscopy with the aid of a chemometric method. Spectroscopic methods are also used in the study of a unique property of the fullerene molecules, namely the formation of microscopic fullerene aggregates (or clusters) in solutions of binary solvent mixtures. By taking advantage of the cluster formation, a new facile photochemical method for the preparation of bulk quantities of polyfullerenes, which are all-carbon polymers of covalently linked fullerene molecules, is developed. The properties of polyfullerenes and related fullerene-containing copolymers are also investigated spectroscopically. |
